Frequency-division duplexing (FDD) transceivers use distinct frequencies to transmit and receive data. Calibrating FDD transceivers is challenging: because the transmitter and receiver units in the transceiver use different frequencies, transmit data cannot simply be looped back to the receiver.
FDD transceivers may be implemented using Quadrature Amplitude Modulation (QAM) transceivers that are sensitive to various signal impairments that affect the quality of the transmitted and received signals. Signal impairments may result from non-idealities in the RF front-ends of the transceivers. For example, mismatched active and passive elements (e.g., quadrature mixers, filters, and/or analog-to-digital converters) in the I and Q (in-phase and quadrature) signal paths introduce I/Q mismatch impairments in transmitted and received signals. I/Q mismatch is present in both the transmitter and receiver.
Accordingly, there is a need for techniques to calibrate FDD transceivers to compensate for signal impairments such as I/Q mismatch.